Gas heater



Sept 18, 1945 I R. wu-:DERKEHR 2,385,177

` GAS HEATER Filed July 1e, 1945 rmentor Gttornegs Patented Sept. 18, 1945 ois css HEATER Robert Wiederkehr, Erlenbach, Switzerland, as signor to Aktiengesellschaft fuer Technische Studien, Zurich, Switzerland, a corporation of' Switzerland v Application July 16, 1943, Serial No. 495,025 In Switzerland January 30, 1942 Claims.

This invention relates to a ses heater, particularly for thermal power plants, in which at least the greater part of e, gaseous working medium, 'preferably air, describes a cycle and is to be heated indirectly by a supply of heat from an external source. f

In plants of this hind the wertung medium has to be heated to 609 C. and even higher. 0n the other hand, the pressure drop to jwhich the working medium is subjected in passing through the heater should be es small es possible, since such a drop greatly impairs the overall emciency oi the plant. The velocity oi the working medium dowing through the heater cannot, therefore, be chosen at will, i. e., oi such a magnitude as would be desirable for ensuring a good heat transmission. .es o. consequence, the danger exists of the leest in that section of the heater which is heated by rnc-listino.

To attain a good emciency in plants of the kind herein referred to, it is further necessary that the heat contained in the combustion gases be utilized to the maximum possible extent; the flue gases should, therefore, leave the heater with as low a temperature as possible.

To meet these dierent requirements and furthermore, to provide o. heater requiring a relatively small heating surface for the transmission ol o. given quantity oi heat, whilst nevertheless odering o, high degree of safety against excessive heating of the materials employed, a heater according to the present invention is so designed thet the working medium, the temperature of which has to be raised, iiows in parallel currents on the one hand through a section of the heater mainly heated by radiation and on the other hand through o. further section heated by contact. Herel'oy, the medium to be heated ows parallel tothe combustion gases through the heater section mainly heated by-radiation and in contrafiow may be so arranged that the ow relationship between the working medium and the products of combustion is concurrent or counterow. In

the most rened embodiment ofthe invention there may be a plurality of surface heaters in a succession of nues. Meansare also contemplated to use waste heat flowing to the stack to heat combustion air flowing to the burner. The burner 4may be ot any known type, using any suitable yface heated by contact is sub-divided into three sections in two of which` the working medium ows in countercurrent relation to the combimtiongases while in the third section, which is the iinal heater, the flow is concurrent. in this embodiment the unal heater is arranged in a horin zontal flue.

Fig. 2 'shows diaatically o. gas heater in which the surface heated by contact is subdivided into two sections which are both accommodated in 'a vertical ilue.

Fig. 3 shows, also diagrammatically, e, gas heater in which the surface heated by contact is likewise subdivided into two sections, one oi which being accommodated in a. vertical flue and the other in a horizontal flue which connects this ue to the combustion chamber.

Fig. 4 shows diagrammatically a similar embodiment to that illustrated in Fig. 3, with the difference, however, that the working medium to be heatedilows parallel to the combustion gases through the section of the 'contact heated surface, which is designed as a tube nest and is am commodated in a horizontal due connected to the combustion chamber.

Referto Figure 1. The numeral l indicates the combustion chamber of a heater used to heat the gaseous medium used in the thermal power plant not shown. In such a. power plant (see forforample the patent to Keller 2,268,074, December 30, 1941) air used as a working medium describes a cycle in which the air is raised in pressure by' '55 pulverized fuel furnace, 5I indicates a crushing mil1 for delivering fuel to the grate, and 4 indicates a source of fuel. As stated, the illustration of the'burner isy purely exemplary and any type of burner using any type of fuel might be substituted.

The combustion chamber I is lined with closely spaced tubes through which the air to be heated flows. The tubes are connected at their bottom to an inlet manifold and at their top to a discharge manifold as shown. Part of the heat is transmitted to the tubes by radiation and a part by conduction from the products of combustion. The tubes 5 are shown as reduced in diameter from their lower to their upper ends, the idea being to secure comparatively free flow to the discharge end of the tubes 5 and impose Whatever flow resistance exists in the circuit at these discharge ends.

The products of combustion leaving the chamber I-pass through a horizontal connecting flue into contact with the surface heat exchanger generally indicated by the numeral 45. Thence the products of combustion ow vertically downward through a flue .I I in contact with another surface heat exchanger generally indicated at 48. Thence the products of combustion pass upward through a second vertical flue 68 to the stack I0, and in their passage through the second vertical flue 48 deliver heat in the order stated to a second stage combustion air heater @39, a preheater tl for the assai?? without requiring excessive pressure drops. In

'consequence an intense exchange oi' heat is sefcover plate 38.

working medium and a iirst stage combustion air heater 50.

Working medium enters through the connection I2 and branches at 6, part of the medium flowing through a connection 6a to the tubes 5 in the combustion chamber Il and the remainder passing through the connection 6b to the exchanger 41, then through the exchanger 46 and from the exchanger 46 to the junction I3. At the junction I3 this medium joins medium which flows through the tubes 5. From the junction I3 the two ow together through the exchanger 45 and thence by way of the connection I4 to the point of use. (In the Keller patent above identifled the ow would be through the pipe there numbered 3.)

Combustion air enters at 9, passes through the primary heater 50, flows thence through the pipe 8 to the secondary air heater 49 and flows thence Y by the connection 2 to a point of use in the burner such as that indicated at 52 or the equivalent. In this way the heat of combustion is usefully applied, and the gases escaping through the stack I0 are at relatively low temperature.

An idea of the performance of the heater may be had from the following centigrade temperatures. Assuming that air enters at I2 at about 300 it is possible to raise its temperature to a value between 500 and 600 in passage through the exchangers 41 and 46 and also in its passage through the tubes 5. The air so heated can be .brought to above 600 by passage through exchanger 45. 'Ihe combustion gases are reduced from about 1000 to a value between 900 and 950 at the entrance to chamber I I. They leave chamber II at a temperature of the order of 550 and they discharge to stack I6 at temperatures as low as 250.

cured under severe conditions, particularly the conditions which exist in the chamber I where the heating is largely by radiation. Since the air flows in parallel through two distinct paths, these paths must be designed to divide the iiow in such a way that the air from the two paths reaches the Junction. point I3 at equal temperatures.

An important feature is the scheme of mounting the final heat exchanger 45 on a removable This has two advantages. It permits the exchanger 45 to be suspended and it permits its ready removal without requiring dismantling of the remainder of the heater.

In the diagrams, Figures 2 to 4 inclusive, alternative arrangements of the final heat exchanger 45 are suggested. To simplify the diagrams exchangers used to heat the combustion air are not illustrated. A primary and a secondary heater such as the parts 50 and 49 of Figure 1 could be used or they could be combined in a' single heater, the particular details of the heater for combustion air being subject to design according to known practice.

Figure 2 shows how the final heat exchanger i5 can be mounted in the upper part of a vertical flue analogous to the flue II of Figure 1.

In Fig. 2 the numeral I5 denotes a combustion chamber and I6 a grate. The working medium to be heated flows'in through a pipe I1 and is led through pipes I8 and I3 into distributors 20 and 2i respectively. The working medium flowing through tubes 22 which are mainly heated by radiation, passes into collecting headers 23 andl heated by contact which lies in the lower temperature range, and thereafter likewise into the collector 25. Hereupon, the whole quantity of working medium flows through a system of tubes 21 forming the second part of said surface heated by contact and in which this working medium is brought to its final temperature, whereafter it then passes to a collector 28 and thence to a consumer B designed as a turbine.

In Figure 2 the working medium iiows through the exchanger 2'I in counterow relation to the combustion gases. In this respect it differs from the arrangement shown in Figure l, but the arrangement of Figure 1 might be modified to secure counterow, and this possibility is diagrammed in Figure 3.

In the embodiment of the invention shown in Fig. 3, the part 29 of the surface heated by contact, through which flows the whole quantity of working medium to be heated and which lies in the range of higher temperature, is arranged in a horizontal flue 30 connecting the combustion chamber 3l to a first vertical ue 32. Reference numeral 33 denotes a second vertical-nue connected in series to said flue 3'2. The section 34 of the surface heated by contact and lying in the range of lower temperature is arranged in the vertical iiue 32. The working medium to be heated iiows through said section 34, as also through the heater section 29 designed as a tube nest, in a counter-current to the combustion gases. Between the two heater sections 29 and 34 a collecting header 35 and a distributing header 36 are arranged. The heating tube nest 231s connected to this distributing header 3B approximately through the passage; connections for supplying gas to be heated to both oi' said exchangers in parallel; a collector for the heated gases iiowing from both said exchangers, said connections and collector being so related to the exchangers that the flow of gases through the multi-pass exchanger is counter-current to the iiow oi products of combustion, the two exchangers being so proportioned that the temperatures of the gases flowing therethrough are approximately equal as the gases reach said collector; and a second multipass tubular heat exchanger located in said passage near its junction with the combustion chamber and arranged to receive gases from said co1- lector and discharge them to a pointof use.

4; A heater intended for heating gases to high temperatures, comprising in combination, means forming a combustion chamber, a horizontal ontake leading laterally from the upper end thereof and a substantially vertical flue leading downward from said `oistake; a single-pass tubular lheat exchanger in said combustion chamber mounted adjacent to the walls of the chamber so as to be heated mainly by radiation; a multi- .pass tubular heat exchanger mounted with its tubes extending across said flue so as to be swept by combustion gases ilowing downward therethrough; means for supplying gas to be heated in parallel to the lower ends of both said exchangers; a collector for the heated gases owing from the upper ends of both of saidrexchangers, the exchangers being so proportioned that the temperatures of gases owing therethrough are approximately equal as the gases reach said collector; and a second multi-pass exchanger located in said oitake and connected to receive gases from said collector and discharge them to a point of use.

5. A heater intended for heating gases to high temperatures, comprising in combination, means forming a combustion chamber, a horizontal odtake leading laterally from the upper end thereof and ak substantially vertical nue leading downward from said offtake', a portion of the enclosing -wall of the said oiltake being removable; a singlepass tubular `heat exchanger in said combustion chamber mounted adjacent to the walls of the chamber so as to -be heated mainly by radiation; a multi-pass tubular heat exchanger mounted with its tubes extending across said flue so as to be swept by combustion gases ilowlng downward therethrough; means for supplying gas to be heated in parallel to the lower ends of both said exchangers; a collector for the heated gases flowing from the upper ends oi.' both of said exchangers, the exchangers being so proportioned that the temperatures of gases owing therethrough are approximately equal as the gases reach said collector; and a second multi-pass' exchanger located in said oiltake and connected to receive gases from said collector and discharge them to a point of use, the last-named exchangerA :being suspended from the removable portion of the offtake wall and being capable of disconnection without disturbing the other exchangers, whereby it is removable for replacement or repair.

ROBERT WIEDm :oor-|- 

